Prior to the present invention, it has been known to prepare catalysts and catalyst supports from pseudoboehmite, particularly by calcination of the pseudoboehmite to aluminum oxide or more specifically gamma alumina. Pseudoboehmite is a material of choice because of its reactivity, availability and forming properties. This material is widely used as a catalyst support and catalyst for many chemical processes.
However, a very particular property of pseudoboehmite derivatives is that they are mainly acidic which is usually useful for catalytic reactions which involve carbo-cation intermediates, such as in alcohol dehydration, skeletal isomerization, ring alkylation, and cracking of hydrocarbons. When they are used as supports, their acidity is usually necessary for activation of a catalytic agent such as nickel, platinum, or molybdenum in a bifunctional mechanism needed for the desired reaction.
Prior to the present invention, it has been known to convert acetone to isophorone and mesityl oxide by condensation in the presence of a catalyst made by reacting (or "interacting") certain aluminum salts with certain magnesium salts or hydroxides--see Reichle, U.S. Pat. Nos. 4,165,339 and 4,458,026. A catalyst described as "Mg-Al-CO.sub.3 Hydrotalcite Catalyst" and similar compositions were proposed in the examples of Reichle,s U.S. Pat. No. 4,458,026, using as ingredients such materials as Mg(NO.sub.3)2.6H.sub.2 O and Al.sub.2 (NO.sub.3)3.9H.sub.2 O together with sodium carbonate. Synthetic hydrotalcites (Joint Committee on Powder Diffraction Standards files #14-191 and 22-700) sometimes also referred to as a magnesium aluminum hydroxy carbonate are also proposed in U.S. Pat. Nos. 4,656,156 and 4,476,324. Other similar catalyst compositions containing magnesium and aluminum are disclosed in U.S. Pat. Nos. 4,539,195 and 4,086,188. Such compositions are not made from the mixed oxides of magnesium and aluminum, however, but generally begin with at least one salt or hydroxide, which affects the crystalline structure of the final composition. The method of "interacting" the salts has become known as the co-precipitation method.
Various mixed oxides are reviewed in Papa's U S. Pat. No. 4,535,187, which contains the statement (col. 1, lines 48-51) "The co-precipitated mixed oxide catalysts have the drawback of exhibiting poor catalyst manufacturing reproducibility and are expensive." The review, however, does not include a discussion of a mixture of aluminum and magnesium oxides.